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Coat Color Genetics ofPeromyscus: II. Tan Streak—A New Recessive
Mutation inthe Deer Mouse, P.maniculatis
L. R. K. Wang, J. P. Crossland, andW. D. Dawson
The first mutant tan streak deer mice ap-peared in the initial
laboratory-bred genera-tion of a stock of Peromyscus
maniculatusnubiterrae collected in Macon County, NorthCarolina.
Laboratory progeny from the origi-nal animals were bred and mated
among
themselves and to wild-type individuals. Thetan streak phenotype
is characterized bynearly complete absence of coat pigmenta-tion,
except for a pale tan patch or narrowstripe extending mid-dorsally
posteriorly fromthe head. The band is frequently somewhatbroader in
the shoulder region, occasionallyforming a cross-shaped pattern.
There is noevidence of black eumelanin in any part ofthe coat. The
eyes are fully pigmented, ap-pearing black, and pigment is present
in theskin of the ears and elsewhere. The trait isinherited as an
autosomal recessive. The ge-netic locus is provisionally designated
tns.Crosses between homozygous tan streak (tns/tns) animals and
albino (c/c), ivory (Hi), non-
Figure 1. (A) Tan streak deer mouse compared with (B) wild
type.
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Table 1. Inheritance of the tan streak (tns) color trait in
Peromyscus maniculatus
Phenotype AnalysisMating class
Female
+ /+ X
tns/tns x
+/tns x
+/tns x
tns/tns x
tns/tns x
Male
tns/tns
+/+
+/tns
tns/tns
+/tns
tns/tns
No. ofmatings
3
2
4
4
5
5
Obs.
Exp.
Obs.
Exp.
Obs.
Exp.
Obs.
Exp.
Obs.
Exp.
Obs.
Exp.
Wild type
Female
22
28.5
4
2.5
27
29.25
16
16.5
7
8
0
0
Male
35
28.5
1
2.5
30
29.25
23
16.5
8
8
0
0
Tan streak
Female
0
0
0
0
13
9.75
16
16.5
10
8
17
21
Male
0
0
0
0
8
9.75
11
16.5
7
8
25
21
RatioX2
dfP
RatioX2
dfP
RatioX2
dfP
RatioX2
dfP
RatioX2
dfP
RatioX2
dfP
Segre-gation
1:0
1:0
3:10.1541.7-.6
1:12.1821.2-.1
1.10.1251.8-.7
0:1
Sex
1:12.9651.10-.05
1:11.81.2-.1
1:10.0511.9-.8
1:10.0611.9-8
1:10.1251.8-7
1:11.5241.3-.2
Inter-action
1:10.82114-.3
1:12.1821.2-.1
1:10.5001.5-.4
Total
3:3:1:11.5903.7-.6
1:1:1:14.4243.3-2
1:1:1:10.7503.9-.8
agouti (a/a) and brown (bib) deer mice pro-duced only wild-type
progeny, indicating thatthe tns mutation is not at any of these
loci.
In 1986 a group of Peromyscus maniculatusnubiterrae (Cloudland
deer mouse) werecaptured in the southern Blue RidgeMountains of
Macon County, North Caro-lina, to establish a small breeding
colonyat Clemson University. All of the founderanimals were wild
type. The following yearthe first tan streak deer mouse, a
male,appeared from a mating between wild-caught animals. The
initial male tan streakanimal was mated with eight females
toproduce wild-type heterozygotes and,subsequently, with his
heterozygous prog-eny to produce other tan streak deer
mice.Heterozygous half-sibs were mated to pro-duce additional tan
streak animals. Themode of inheritance was determined fromthese and
subsequent crosses. Additionaltan streak animals were bred at the
Uni-versity of South Carolina Peromyscus Ge-netic Stock Center and
were crossed to P.m. bairdii stock to improve fertility. Fur-ther
formal genetic analysis was conduct-ed at the Stock Center, where a
line ofthese animals continues to be maintained.
DescriptionThe tan streak trait is evident within a fewdays of
birth, since the affected deer miceare markedly paler in color than
their wild-
type counterparts. The phenotype is fullyexpressed by weaning.
Superficially, thecoat is white with a pale tan streak ex-tending
along the mid-dorsal line from abroader tan patch in the shoulder
region(Figure 1). The patch with the dorsal streakforms a cross
pattern in some animals. Thedorsal stripe may be much abbreviated
insome specimens and evident only in thecervical area, while in
others it may extendto the base of the tail. Typically the
streakextends about one-half to two-thirds thelength of the
body.
Microscopic examination of hairs fromthe pigmented mid-dorsal
stripe shows thatthe stripe contains mostly hairs with
sparsetan-yellow pigment granules along thelength, but the pigment
is somewhat moreconcentrated in the distal 40%. There isno distinct
agouti band. However, con-strictions in the individual hairs are
pres-ent. The pigment has more an aspect ofbrown eumelanin than of
phaeomelanin.Some hairs have occasionally large pig-ment clumps. A
minority of hairs in thestripe are devoid of pigment. A given
hairtends to contain color granules along mostof its length, or
else not at all. Pigment iscompletely absent in the lateral white
por-tion of the coat.
The eyes are fully pigmented. The earsand tail stripe are
pigmented but are muchpaler and more tan than in the wild type.The
scrotum is also lightly pigmented.
Tan streak deer mice are not deaf. Theyrespond to auditory
stimuli, unlike severalother partially white coat color mutants
inmammals (Searle 1968; Silvers 1979).
InheritanceTan streak is inherited as a simple auto-somal
recessive trait (Table 1). No signif-icant deviations (.05 level)
from the ex-pected ratios were observed among the 23matings and 280
progeny classified. Bothwild-type males and mutant females
wereproduced from backcrosses between mu-tant females and
presumptive heterozy-gous males, thus excluding sex linkage.
Nosignificant interaction between sex andphenotype was
detected.
Interactions with four other recessivecoat color mutations in
Peromyscus weretested (Table 2). Crosses between tanstreak and
homozygous albino (c/c), ivory(//()• nonagouti (a/d), and brown
(6/6)color mutants produced wild-type proge-ny in each instance,
indicating that tns isnonallelic with genes for these pelage
col-ors.
Forty-nine F2 progeny from the tan streakx non-agouti cross (F,
= +/tns +/d) weretyped for coat color upon speculation thata "black
streak" interaction phenotypemight be produced, since such a
variantwas recently observed in the white-footedmouse, P. leucopus
(see Discussion). Noblack streak animals occurred among the
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Table 2. Tests for allellsm between tan streak and other coat
colors in P. maniculatus
Cross N,_ , No. of progeny obtained
Female MaleNo. ofmatings Wild type Mutant
Tan streakIvory (i/i)Tan streakTan streak
albino (c/c)tan streaknonagouti (.a/a)brown (6/6)
3111520
F2's, although three were expected. How-ever, the phenotypic
ratio from the crosswas 25 wild type: 6 nonagouti: 11 typicaltan
streak: 7 diffuse tan. The latter pheno-type at weaning appeared
somewhatgrayish-tan, later molting to a diffuse paleorange tan,
over much of the head, back,and shoulders without a distinct
mid-dor-sal streak. The observed phenotypes areconsistent with a
9:3:3:1 Mendelian ratio(X2 = 6.76, .2 > P > .1); or a 9:3:4
ratio ifthe tan streak and diffuse tan phenotypesare pooled (x
2 = 4.04, .2 > P> .1). Delim-itation of "tan streak" from
"diffuse tan"is not absolute, since classification of
someindividuals is arbitrary. Under the as-sumption that no
nonagouti tan streak an-imals were represented in the F2, the
de-viation from the expected is highlysignificant (x
2 = 12.86, P < .005). Appar-ently, the tan streak phenotype
is essen-tially epistatic to the agouti locus, sincenonagouti tan
streak animals cannot beidentified with certainty from agouti
tanstreak individuals.
Discussion
Tan streak is a newly detected locus in thedeer mouse and
differs from any other pre-viously described mutant phenotype in
thisspecies. Among known color loci in Pero-myscus, albino (c),
ivory (/), and brown(ft) were considered possibly homologouswith
the tan streak locus. In the deer mouse,as in other mammals, true
albinism is dueto an autosomal recessive gene (c) (Sum-ner 1922),
which results in the absence oftyrosinase activity (Foster and
Barto 1963).In other species, but not in Peromyscus,additional
mutant alleles occur at the clocus, including c" in Himalayan
rabbitsand Siamese cats, and c°h in chinchilla rab-bits. These
additional alleles produce par-tially pigmented animals, but the
colortends to be concentrated on the extremi-ties, unlike the
situation in tan streak(Searle 1968).
The ivory mutation (/) in Peromyscus alsoproduces extremely
diluted, nearly allwhite animals. Ivory is also inherited asan
autosomal recessive trait (Huestis 1938).
Unlike albino, ivory deer mice have an off-white pelage with the
base of the fur slight-ly beige-gray. Albino and ivory
representdistinct loci with complementarity be-tween the wild-type
alleles (Huestis 1938).Thus, the albino (c/c + / + ) x ivory (+
/+i/i) cross produces all wild-type (+/c +/0 Fi progeny, as does
the cross of tanstreak animals with either of these vari-ants.
The brown mutation (ft) has been re-covered several times in
Peromyscus(Dawson et al. 1969; Homer and Dawson1993) and
phenotypically is like brown inMus and Rattus. The brown mutation
ap-parently affects the amount of melaninsynthesized from
3,4-dihydroxyphenyla-lanine (DOPA) relative to 5,6-dihydroxy-indole
(Murray et al. 1983). Since onlybrown melanin granules occur in tan
streakanimals, and tan streak apparently doesnot interact with
nonagouti to produceblack melanin, the action of the tan
streakmutation resembles brown. However, theextensive white on
these animals is nottypical of brown locus variants in otherspecies
(Searle 1968; Silvers 1979). Theabsence of allelism between tan
streak andbrown, ivory, albino, and agouti suggestsa mode of action
different from any of these.
Hooded (/?//?) is a recessive variant inrats (Rattus norvegicus)
that shares somephenotypic similarity to tan streak (Searle1968).
The extent of the dorsal streak com-mon in hooded rats varies
greatly de-pending on background modifiers, and thespecific color
of the streak is determinedby the other pigmentation factors
present(Weisbroth 1969). Thus in hooded rats withotherwise
wild-type coat color factors, thestreak (and hood) would be the
undilutednormal agouti pattern. In this respect tanstreak differs
from hooded in that thestreak is extremely diluted with no
evi-dence of normal agouti hairs.
A white-footed mouse (P. leucopus~) witha dark blackish streak
was recently foundin a captive stock by George Smith (per-sonal
communication). Except for the col-or of the streak, this mouse had
a phe-notype resembling tan streak. The deermouse and white-footed
mouse are not in-
terfertile; thus, it is not possible to directlytest these two
variants for allelism.
Originally, this mutant was informallydesignated "tan mane," but
"tan streak"better describes its typical expression.Therefore, the
designation tan streak(symbol tns) is proposed for this locus.From
the Department of Zoology, Clemson University,Clemson, South
Carolina (Wang), and the Departmentof Biological Sciences,
University of South Carolina,Columbia, South Carolina 29208
(Crossland and Daw-son). A portion of this study was conducted at
thePeromyscus Genetic Stock Center, which is supported,in part, by
NSF grant no. DIR-9000352. We thank J.Barnsdale for his assistance
in organizing the data andC. Joyner, J. Ruff, and A. Lawson for
providing excel-lent animal care. Photographs by C. Cook.
Reprintsshould be requested from Dr. Dawson at the
addressabove.
The Journal of Heredity 1993:84(4)
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